This invention relates to an improved closure for food containers, and particularly to those used for the home canning of foods, and to a method of canning using that closure.
Many types of containers and closures for the home canning of food products have been developed over the years. For many years, the most prevalent home canning medium in the United States has been the so-called "Mason Jar." Such a medium usually comprises a glass container having a standardized external thread on the periphery of the mouth and a suitable cap or closure assembly. Most recently, a widely used two-piece closure assembly has comprised a dished, disc-shaped central cover panel having an annular gasket formed at its periphery on one surface and a threaded peripheral portion. The threaded peripheral portion has a depending skirt or flange with a suitable thread, cooperable with the glass container thread, and an annular shoulder adapted to overlie the upper periphery of the gasketed central cover panel. The threaded peripheral portion is usually loosely threaded on the container after the central cover panel has been positioned over the mouth and prior to heating. The threaded peripheral portion is usually left loose enough so that, as the contents are heated, venting of gases may take place under the gasket. Thereafter, as the container cools the central cover panel seals against the container lip, following which the threaded peripheral portion is tightened so that when the container is stored, vacuum will be positively maintained. When the cover panel is of the dished type, as the container cools, the panel snaps into an inwardly dished position. Other systems for sealing home canning containers have used separate rubber sealing gaskets or rings, and the like.
All of the various media and methods for sealing home canning containers have one or more drawbacks. Some systems require separate and separable sealing elements, such as rubber gaskets or rings. Other require elaborate positive locking mechanisms. The most commonly used system usually requires the use of an implement to remove the sealed central cover panel from a container. Such removal damages the gasketed central cover panel and therefore requires it to be discarded after a single use.
In my copending parent application Ser. No. 572,160, filed Apr. 28, 1975, an invention is disclosed relating to a one-piece reusable closure for home canning. The closure comprises a threaded lid with a bonded annular closed-cell foam gasket at the periphery of a central portion of the lid for confronting and sealing against a jar lip. To provide a means for gas to escape from the jar during heating in the canning process, the gasket is designed to be compressed by the gas pressure to permit venting of the gas between the jar lip and the gasket. To insure that the gasket will always have a suitable compression capability, special limitor projections extend from the periphery of the central portion of the lid, at spaced intervals, downwardly into the gasket and compress the gasket material against the jar lip to control tightening of the lid on the jar. This leaves circumferentially spaced portions of the gasket between the limitor projections in a less compressed state and therefore capable of further compression by increased gas pressure to provide venting as necessary.
It was then found that limitation of the compression of the gasket can be achieved in other novel ways. In my copending Application Ser. No. 691,564, entitled "Canning Closure and Method" filed concurrently herewith, an invention is disclosed in which other limitor means are provided to prevent overtightening of the closure and over-compression of the gasket material to the point where gases cannot vent therethrough. Preferably such limitor means are formed in the skirt of the closure. In one embodiment, the limitor means comprises a deformed portion of the closure skirt thread providing a threading stop for abutment with a leading portion of the container thread. In another embodiment, a portion of the lower edge of the closure skirt abuts a circumferential flange on the glass container. In either case, the closure is prevented from being screwed further onto the container and thus, the gasket is compressed only to a predetermined extent.